Why have the Americans developed space shu
题型：单项选择题
问题：
Why have the Americans developed space shuttle according to the passage
A．It is a first step to explore outer space.
B．It is a follow-up action of the Apollo moon landings.
C．It is a compromise to the exorbitant human expeditions to the Mars.
D．It is a compensation for the wishful thinking of human landing on the Mars.